Doctoral Degrees (Chemistry and Polymer Science)
Permanent URI for this collection
Browse
Browsing Doctoral Degrees (Chemistry and Polymer Science) by browse.metadata.advisor "Cloete, Thomas Eugene"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- ItemElectrospun antimicrobial and antibiofouling nanofibres(Stellenbosch : Stellenbosch University, 2011-12) Gule, Nonjabulo Prudence; Klumperman, Bert; Cloete, Thomas Eugene; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The main objective of this study was to develop electrospun nanofibres with both antimicrobial and antibiofouling properties for possible application in water filtration. To do this, two routes were investigated: firstly, the use of biocides and bactericidal copper salts to introduce bactericidal properties on electrospun nanofibres. Secondly, the modification of polymers using furanone compounds to obtain nanofibres with the ability to repel microbial attachment. Fabrication of biocide-containing PVA nanofibres was successful. This was achieved through direct doping of PVA solutions with AquaQure which is an aqueous biocide comprising of mainly Cu2+ and Zn2+, prior to the electrospinning process coupled with chemical crosslinking using glyoxal. The conventional needle based electrospinning technique was used to fabricate these nanofibrous mats. The presence of the constituents of AquaQure on surfaces of PVA/AquaQure nanofibrous mats was confirmed using energy dispersive x-ray analysis (EDX). ATR/FTIR, XRD, TGA, DSC and SEM techniques were used to do chemical and thermal analysis of the nanofibres in comparison with pristine PVA nanofibres. These nanofibres demonstrated antimicrobial activity of up to 5 log against the Gram-positive strain S. aureus Xen 36 and Gram-negative strains E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 and K. pneumoniae Xen 39. Because of crosslinking, these fibres also demonstrated good water stability. Leaching of the ions constituting AquaQure was limited and compared with South African national standards for drinking water, the water filtered through these nanofibress was deemed safe for human consumption. Bioluminescence imaging and fluorescence microscopy were used to confirm antimicrobial activity results obtained from plate counting. These nanofibres demonstrated satisfactory antimicrobial efficiency but did not repel microbial attachment. The second part of this study entailed the investigation of copper-doped PVA and SMA nanofibres for antimicrobial activity. Although bactericidal properties of copper are well documented, its selection was based on the fact that it is the main constituent of the AquaQure. Bubble electrospinning was used instead of needle electrospinning to upscale nanofibre production. Similar techniques as those used in PVA/AquaQure nanofibres were used to characterize the copper functionalized nanofibres. Even though these nanofibres demonstrated exceptional antimicrobial efficacy (up to 5 log) for all the strains, bioluminescence imaging indicated a trend for these cells to enter a dormant state on contact with the copper containing-nanofibres. The last part of this project involved testing of free furanone compounds as well as surface-tethered furanone-modified nanofibres for their antibiofouling potentials. To do this, blends of 2,5-dimethyl-4-hydroxy-3(2H)furanone (DMHF) (5% wt/vol) with PVA (10% wt/vol) were prepared and electrospun to produce PVA/DMHF nanofibres. The free furanones and furanone-modified nanofibres demonstrated not only antibiofouling properties but also antimicrobial activity. Other furanone compounds with 3(2H) and 2(5H) cores were synthesized. The synthesis of these furanone compounds (5-(2-(2-aminoethoxy)ethoxy)methyl)-2(5H)furanone and 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone) was successful. Their structures and molar masses were confirmed using 1H NMR and ES mass spectroscopy. These furanones were then covalently immobilized on the SMA backbone. To test their antimicrobial and antibiofouling activity, the furanone-modified polymer was dissolved in an ethanol and methanol mixture (1:1) and electrospun to produce nanofibres. The free furanone and furanone-modified SMA nanofibres derived from 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone demonstrated high antibiofouling and antimicrobial efficiency against the Gram-positive strain S. aureus Xen 36 and Gram-negative strains E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 and K. pneumoniae Xen 39. The 2(5H) furanone on the other hand had limited activity against the strains. These nanofibres were also characterized and compared with their pristine polymer counterparts and leaching experiments were conducted using GC-MS.
- ItemStrategies for antibiofouling membranes(Stellenbosch : Stellenbosch University, 2015-03) Cloete, William Joseph; Klumperman, Bert; Cloete, Thomas Eugene; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Membrane filtration is increasingly used for municipal and industrial wastewater treatment because it is an effective way to filter out bacteria and organic compounds. One of the largest problems is biofouling of the membranes, which may lead to blockage of the membrane with organic biofilms. Such blockages require expensive interruptions to the filtration process for periodic cleaning and cause a decrease in membrane lifespan. The ideal solution to the biofouling problem would be the production of novel polymeric membranes that do not biofoul. Theoretically, this can be accomplished in two ways: (1) provide membrane surfaces to which bacteria and organic material are incapable of adhering, and (2) introduce reactive compounds on the membrane surface that degrade the biofilm. In four data chapters written in the format of stand-alone publications, techniques were explored for the production of inherently anti-fouling membranes using the most current strategies of polymer synthesis and characterization. Specifically, Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization is employed to graft an anti-adhesive layer of hydrophilic copolymer chains onto the surface of regenerated cellulose membranes. Then, the mechanism of control of the polymerization reaction of the hydrophilic copolymers was investigated in enable design of an optimized anti-adhesive surface layer. In the following two chapters, immobilization of different combinations of biomoleculedegrading enzymes on high surface area non-woven nanofibrous mats, produced via electrospinning, was investigated. The retention of their enzymatic activity was tested in order to first prove the principle that enzymes can retain activity once immobilized on a substrate. In the subsequent chapter two additional enzymes commonly used for biofilm remediation in clean-in-place (CIP) processes were immobilized on the nanofibers, on their own as well as in combination with each other. Surface modification of regenerated cellulose membranes to introduce zwitterionic hydrophilic copolymers revealed that grafting of copolymers of N-vinylpyrrolidone (NVP) and maleic anhydride (MAnh) could be achieved through an R-group approach of RAFTmediated polymerization. The MAnh contained in the polymer backbone or as end-groups of the polymer were converted to zwitterionic compounds. Upon exposure to bacteria, these membranes prevented adhesion of extracellular polymeric substances (EPS) and bacteria cells to the membrane surface. An investigation into the underlying kinetics of RAFTmediated polymerization showed that no control was achieved for 1:1 monomer ratios of NVP/MAnh for two types of RAFT agents. The lack of control was due to the acid-catalyzed dimerization of NVP occurring at a very large extent. Copolymerization was affected at even small amounts of MAnh but, once consumed, an initialization step for NVP was observed. This provides a means of incorporating short segments of the functional MAnh monomer in the copolymer whilst maintaining reasonable control over the polymerization using RAFT chain transfer agents. As an alternative to anti-cell adhesive surfaces, immobilization of enzymes on nanofibrous mats holds promise for the in situ degradation of organic biofilms. First, horseradish peroxidase and glucose oxidase were immobilized via nucleophilic addition of primary amines of the enzyme to reactive maleic anhydride residues in the copolymer backbone to prove the principle and illustrate that cascade reactions can be performed with catalytically active immobilized enzymes. Next, the combined immobilization of protease and α-amylase, two enzymes commonly used for biofilm remediation, enabled the degradation of protein and starch solutions. Co-immobilization led to an unexpected increase in activity of the αamylase, but at the same time a significant decrease in protease activity. The results obtained from the strategies explored in this thesis bode well for the future of manufacturing inherently anti-biofouling membranes and may very well lead to making membrane filtration economically more feasible to produce safe potable water, especially in the developing world.